Between this and the "one hour adventure" article, it sounds to me like they are playing with what the smallest unit of playing time is for a session. I think this is a good thing. People who play longer sessions can just stack some multiple of this smallest unit together. However, if they shoot for designing around a 4 hour "typical" session, that means that 2 hour groups are fighting a much steeper uphill battle.
Okay that is a completely different design goal and honestly a completely different question they could be asking to fulfill that goal.
Q: What is the minimum amount of time you would sit down and play DnD
1: 30 mins
2: 1H
3: 2H
4: 4H
5: 6H
6: 8H
7: 10H
8: 12H
9: 12H+
I could understand saying 2 hours if we are talking about the minimum. But the question was how long, at 2 hours a go, should it take to get to level 10. That is a radically different question and deserves a different response. As I have never successfully played 2 hours at a time, weekly or otherwise, I can only approximate based on what I have played - which I did.
On a side note, I'm sure they are going to make the effort to accommodate me, the 2 hour people and the years long people. The problem I foresee is them putting most of their time accommodating the 2h/week for 4-6 week people and ignoring the rest of us.
I don't want a new level every 3 hours. I don't I don't I don't. I can barely imagine getting a new level every 1.5 sessions (or 2). Getting a new level every 3 sessions seems quick to me, magnify that feeling if the sessions are only 2 hours long. That will mean I'm gaining a level for very little work.
Also, on another note, this is DnD. I want it to take AT LEAST as long as an RPG video game. The problem is, with this question, that I'm playing a session that is shorter than my game of clue, monopoly or poker.
For me, DnD =/= a game of cards and the length of a game of cards shouldn't be the default they put their time working on.